Micro and nanofiber nonwoven spunbonded fabric

ABSTRACT

The invention provides methods for the preparation of nonwoven spunbonded fabrics and various materials prepared using such spunbonded fabrics. The method generally comprises extruding multicomponent fibers having an islands in the sea configuration such that upon removal of the sea component, the island components remain as micro- and nanofibers. The method further comprises mechanically entangling the multicomponent fibers to provide a nonwoven spunbonded fabric exhibiting superior strength and durability without the need for thermal bonding.

FIELD OF THE INVENTION

The invention relates to micro- and nanofibers and fabrics prepared fromsuch fibers. More particularly, the invention relates to nonwovenspunbonded fabrics prepared using micro- and nanofibers.

BACKGROUND

There is an ongoing search in the textiles field for high strengthnonwoven materials. In particular, there is a growing need in the artfor nonwoven materials comprising microfibers and/or nanofibers.

Fabrics composed of micro- or nanofibers offer small pore size and largesurface area. Thus, they generally bring value to applications wheresuch properties as sound and temperature insulation, fluid holdingcapacity, softness, durability, luster, barrier property enhancement,and filtration performance are needed. In particular, products intendedfor liquid and aerosol filtration, composite materials for protectivegear and clothing, and high performance wipes could benefit greatly fromthe introduction of such small fibers.

Manufacturing techniques associated with the production of polymericmicro- and nanofibers are electrospinning, meltblowing, and the use ofmulticomponent fibers, such as segmented pie and islands-in-the-sea(I/S) fibers. In electrospinning, a fiber is drawn from a polymersolution or melt by electrostatic forces. This process is able toproduce filaments with diameters in the range from 40 to 2000 nm.Meltblowing processes are capable of producing fibers having diametersof 0.5 μm to 10 μm. Even though filaments measuring 0.5 μm can beobtained via this technique, most commercially available meltblown mediaare generally about 2 microns and above.

In general, meltblowing and electrospinning produce nonwoven mats ratherthan single fibers and these mats consist of fibers characterized by lowstrength. Thus, electrospun or meltblown fiber webs are typically laidover a suitable substrate that provides appropriate mechanicalproperties and complementary functionality to the fabric. Moreover,existing meltblowing processes are not able to produce nanofiber webseasily, and they can process only a limited number of polymers.Electrospinning, on the other hand, is able to make nanofiber mats withsubstantially smaller fibers than meltblown or spunbonded webs; however,this process has very low productivity.

With multicomponent fibers, the I/S approach can produce significantlysmaller fibers than the segmented pie technique, however the sea in theI/S fibers has to be removed, and this often creates an environmentalissue. Also, since virtually all spunbonds are thermally bonded,subsequent removal of the sea component from thermally bonded substratesgenerally results in the loss of structure as a result of disintegrationof the bond spots. In other words, the art has heretofore failed toprovide methods for producing I/S spunbond webs that provide highstrength and retain integrity after removal of the sea component. Thus,I/S spunbond webs require an alternative means of bonding the structurein place of thermal bonding.

Because of the above mentioned shortcomings, there are no commercialproducts available today based on the spunbond I/S technology. Thepresent invention fills such void in the market for the production oflarge volumes of micro- and nanofiber webs.

SUMMARY OF THE INVENTION

The present invention provides nonwoven, spunbonded fabrics preparedusing micro- and nanofibers. Such fabrics exhibit high strength anddurability while maintaining a relatively low basis weight (i.e., weightper unit area of fabric). Moreover, the fabrics prepared according tothe invention further exhibit improved mechanical properties, such astensile strength and tear strength. Surprisingly, all of these advancesare achieved without the necessity of thermal bonding, as is normallyassociated with spunbonded fabrics.

In one aspect, the invention is directed to a method of preparing anonwoven spunbonded fabric. The fabric can be of varying dimensions andvarying web weights while still maintaining the valuable propertiesdescribed herein. In one embodiment, the method of the inventioncomprises extruding continuous multicomponent fibers, forming aspunbonded web, and mechanically entangling the multicomponent fibers inthe web to form a nonwoven spunbonded fabric. The multicomponent fiberspreferably have a predetermined average diameter and are extruded tohave an islands in the sea configuration. Generally, the I/Smulticomponent fibers comprise a plurality of island componentssurrounded by a sea component. In specific embodiments, the islandcomponents comprise a first polymer and the sea component comprises asecond polymer. The first polymer and the second polymer can comprisethe same or different polymer. Moreover, the first and second polymerscan each comprise a single polymer or can comprise mixtures of polymers,including homopolymers, copolymers, and terpolymers.

The method of the invention can comprise process steps generallyassociated with spunbonding. For example, the extruding step cancomprise one or more of the following steps: spinning the multicomponentfiber through a die; quenching the spun fibers, such as with forced air;attenuating a plurality of extruded fibers; laying (such as in a randommanner) the extruded fibers onto a surface, particularly a movingsurface, such as a forming belt, to form a nonwoven material; moving thenonwoven material through one or more compaction rollers; and windingthe nonwoven material onto a roll, such as a winder.

The method of the invention can also include further process steps. Inone embodiment, the method further comprises thermally bonding themulticomponent fibers. For example, the multicomponent fibers can beextruded and laid on a forming belt and then moved through a calendaringdevice, or any other type of device useful for providing heat generallyor at discrete points across a surface of the nonwoven materialsufficient to at least partially melt a portion of the nonwoven materialand thus thermally bond the nonwoven web at one or more points.

In further embodiments, the method can also comprise removing the seacomponent of the multicomponent fiber. For example, the fibers can besubjected to a water and/or chemical treatment using reagents capable ofdissolving or otherwise breaking down the material used in making thesea component. Preferably, the treatment used to remove the seacomponent does not adversely affect the island components, which shouldbe left substantially intact after removal of the sea component. Stillfurther, the method of the invention can comprise subjecting thespunbonded fabric to certain processing steps after removal of the seacomponent. For example, the method can comprise thermally bonding atleast a portion of the island components. Such thermal bonding cancomprise any useful method, including methods used for thermal bondingof a multicomponent fiber prior to removal of the sea component, such ascalendaring

The method of the invention is particularly useful in that it providesfor preparation of the multicomponent fiber according to certainspecifications such that desired fiber size can be achieved whilemaximizing mechanical properties of the fibers. For example, in certainembodiments, the multicomponent fiber can be described as comprising anouter surface, which is generally formed of the sea component of themulticomponent fiber. Preferentially, the sea component completelysurrounds island components such that none of the island components formany portion of the outer surface of the fibers. In other words, none ofthe island components protrude through the sea component to be inphysical connection with the ambient environment outside the fiber.

In specific embodiments, the sea component completely surrounds theisland components such that the sea component forms a sheath around theisland components. The sheath can be described as having a measurablethickness between the outer surface of the multicomponent fiber and theislands nearest the outer surface of the multicomponent fiber. Forexample, the island components can be arranged inside the sea inconcentric circles or rings. As such, the most outer ring would comprisethe islands nearest the outer surface of the overall fiber, and the seacomponent would be present to form a sheath exterior to the outer ringof islands. In such embodiments, the sea component can also be presentaround and between the multiple island components within themulticomponent fiber. Preferably, the sheath formed around the outercircumference of the multicomponent fiber has a thickness that isgreater than or equal to an average diameter of the island components.For example, in embodiments wherein the island components have anaverage diameter of 200 nm, the sheath formed by the sea componentpreferably has a thickness of at least about 200 nm, and in embodimentswherein the island components have an average diameter of 800 nm, thesheath preferably has a thickness of at least about 800 nm.

In various embodiments of the invention, the island components of themulticomponent fiber can be prepared to have a variety of diameters.Preferably, the multicomponent fibers are prepared such that all of theislands within a given fiber have a substantially uniform diameter. Ofcourse, the invention also encompasses embodiments wherein islandswithin the same fiber have different diameters. Generally, themulticomponent fibers of the invention can be prepared to compriseislands having an average diameter in the range of about 50 nm to about5 μm. In preferred embodiments, the islands have an average diameter inthe range of about 100 nm to about 800 nm.

The average diameter of the island components within the multicomponentfiber can depend upon the overall diameter of the multicomponent fiberas well as the number of island components present within a givenmulticomponent fiber. Generally, increasing the number of islands withinthe multicomponent fiber naturally reduces the average diameter of theislands within the fiber given a fixed cross-sectional area forcontaining the islands. Although as few as two islands can be prepared,the method of the invention allows for preparation of multicomponentfibers comprising a relatively large number of islands. In preferredembodiments, the multicomponent fiber comprises between about 36 andabout 400 island components. However, an even greater number of islandscan be prepared according to the invention, such as up about 1000islands within a given multicomponent fiber.

The method of the invention is particularly characterized in that itallows for the preparation of a nonwoven spunbonded fabric using I/Smulticomponent fibers without the need for thermal bonding. This avoidsthe reduction in web integrity that typically accompanies removal of thesea component. This is achieved according to the present inventionthrough use of mechanical entangling methods. Specifically, after theextruded fiber is laid on a surface to form a nonwoven web, the nonwovenweb is subjected to mechanical entangling means to interconnect themultiple multicomponent fibers present. Thus, the entangled, nonwovenweb is provided with physical integrity and strength from the multiplecross-over points within the entangled web. Moreover, when the seacomponent is later removed, the various micro- and nanofibers leftbehind (i.e., the island components of the multicomponent fiber) remainentangled and form a nonwoven, spunbonded fabric prepared without theneed for thermal bonding. Various methods can be used according to theinvention to mechanically entangle the fibers. For example, the step ofmechanically entangling the multicomponent fibers can comprise a methodselected from the group consisting of hydroentangling, needle punching,steam jet entangling, and combinations thereof.

The multicomponent fiber of the invention can be prepared using variouspolymers for the island components and the sea component. Preferably,the polymer used for the island components is different from the polymerused for the sea component. In a preferred embodiment, the islandcomponents comprise a polyamide polymer, such as nylon, and the seacomponent comprises a polymer such as poly(lactic) acid (PLA).

In further aspects, the present invention provides a variety of productsprepared according to the method of the invention. For example, in oneembodiment, the invention provides a nonwoven spunbonded fabric preparedaccording to the method described herein. Such fabrics in turn find usein a variety of fields, such as filter products and barrier textiles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an apparatus for preparation of aspunbonded material useful according to one embodiment of the invention;

FIG. 2 is a top perspective view of an islands in the sea multicomponentfiber according to one embodiment of the invention showing across-section of the multicomponent fiber as well as a cut-out sectionof the fiber;

FIG. 3 is a scanning electron micrograph (SEM) image of an I/Smulticomponent fiber prepared according to known techniques whereinisland components form a portion of the outer surface of themulticomponent fiber;

FIG. 4 is an SEM image showing (in cross-section) multicomponent fibersprepared according to one embodiment of the present invention having 18island components, all of which are completely surrounded by a sheathformed by the sea component;

FIG. 5 is an illustration of a process for hydroentangling according tocertain embodiments of the invention using a drum entangler;

FIG. 6 is an SEM image showing a multicomponent fiber according to oneembodiment of the invention having the sea component partially removedto reveal the individual island components;

FIG. 7 is a chart illustrating the relationship between the averagediameter of the multicomponent fiber, the number of islands formedwithin the fiber, and the average diameter of the islands;

FIG. 8 is another chart illustrating the relationship between theaverage diameter of the multicomponent fiber, the number of islandsformed within the fiber, and the average diameter of the islands;

FIG. 9 is an SEM images showing (in cross-section) multicomponent fibersprepared according to one embodiment of the invention having 36 islandcomponents;

FIG. 10 is an SEM images showing (in cross-section) multicomponentfibers prepared according to one embodiment of the invention having 108island components;

FIG. 11 is an SEM images showing (in cross-section) multicomponentfibers prepared according to one embodiment of the invention having 216island components;

FIG. 12 is an SEM images showing (in cross-section) multicomponentfibers prepared according to one embodiment of the invention having 360island components;

FIG. 13 is a chart illustrating absorbent capacity in a nonwovenspunbonded materials according to certain embodiments of the inventionas a function of the number of islands formed in the multicomponentfibers;

FIG. 14 is a chart illustrating absorbency rate in a nonwoven spunbondedmaterials according to certain embodiments of the invention as afunction of the number of islands formed in the multicomponent fibers;

FIG. 15 is a chart illustrating air permeability in a nonwovenspunbonded materials according to certain embodiments of the inventionas a function of the number of islands formed in the multicomponentfibers;

FIG. 16 a is a chart illustrating the crystallinity of the nylon-6 phaseof nylon-6 homocomponent fibers and nylon-6/PLA multicomponent fibersprepared according to certain embodiments of the present invention as afunction of the number of island components for different polymerratios;

FIG. 16 b is a chart illustrating the crystallinity of the PLA phase ofPLA homocomponent fibers and nylon-6/PLA multicomponent fibers preparedaccording to certain embodiments of the present invention as a functionof the number of island components for different polymer ratios;

FIG. 17 a is a chart illustrating the crystalline orientation of thenylon-6 phase of nylon-6 homocomponent fibers and nylon-6/PLAmulticomponent fibers prepared according to certain embodiments of thepresent invention as a function of the number of island components fordifferent polymer ratios;

FIG. 17 b is a chart illustrating the crystalline orientation of the PLAphase of PLA homocomponent fibers and nylon-6/PLA multicomponent fibersprepared according to certain embodiments of the present invention as afunction of the number of island components for different polymerratios;

FIG. 18 is a chart illustrating the tenacity of nylon-6/PLAmulticomponent fibers prepared according to certain embodiments of thepresent invention as a function of the number of island components fordifferent polymer ratios;

FIG. 19 is a chart illustrating the initial modulus of nylon-6/PLAmulticomponent fibers prepared according to certain embodiments of thepresent invention as a function of the number of island components fordifferent polymer ratios;

FIG. 20 is an SEM image of a hydroentangled fabric before removal of thesea component prepared according to one embodiment of the inventionusing multicomponent fibers having 216 island components;

FIG. 21 is an SEM image of a hydroentangled fabric before removal of thesea component prepared according to one embodiment of the inventionusing multicomponent fibers having 360 island components;

FIG. 22 is a chart illustrating the tenacity of nylon-6 fibers asislands remaining from a nylon-6/PLA multicomponent fiber preparedaccording to certain embodiments of the present invention after removalof the PLA sea as a function of the number of islands formed in theoriginal multicomponent fiber;

FIG. 23 is a chart illustrating the initial modulus of nylon-6 fibers asislands remaining from a nylon-6/PLA multicomponent fiber preparedaccording to certain embodiments of the present invention after removalof the PLA sea as a function of the number of islands formed in theoriginal multicomponent fiber;

FIG. 24 is an SEM image of the hydroentangled fabric from FIG. 20 afterremoval of the sea component;

FIG. 25 is an SEM image of the hydroentangled fabric from FIG. 21 afterremoval of the sea component;

FIG. 26 is a chart illustrating island diameter after removal of the seacomponent as a function of the number of islands originally present inthe multicomponent fiber;

FIG. 27 a is a chart illustrating machine direction tensile strength ofa fabric prepared according to certain embodiments of the inventioncomprising nylon-6 fibers as islands remaining from a nylon-6/PLAmulticomponent fiber that was hydroentangled and subjected to removal ofthe PLA sea;

FIG. 27 b is a chart illustrating cross-machine direction tensilestrength of a fabric prepared according to certain embodiments of theinvention comprising nylon-6 fibers as islands remaining from anylon-6/PLA multicomponent fiber that was hydroentangled and subjectedto removal of the PLA sea;

FIG. 28 a is a chart illustrating cross-machine direction tear strengthof a fabric prepared according to certain embodiments of the inventioncomprising nylon-6 fibers as islands remaining from a nylon-6/PLAmulticomponent fiber that was spunbonded and subjected to removal of thePLA sea;

FIG. 28 b is a chart illustrating machine direction tear strength of afabric prepared according to certain embodiments of the inventioncomprising nylon-6 fibers as islands remaining from a nylon-6/PLAmulticomponent fiber that was spunbonded and subjected to removal of thePLA sea;

FIG. 29 is an SEM image of a fabric prepared according to one embodimentof the invention using an I/S fiber that was hydroentangled, subjectedto removal of the sea component, and calendared;

FIG. 30 is an SEM image of a fabric prepared according to one embodimentof the invention using an I/S fiber that was hydroentangled, calendared,and then subjected to removal of the sea component;

FIG. 31, is a detailed view of one bond point of the fabric illustratedin FIG. 29; and

FIG. 32 is a detailed view of one bond point of the fabric illustratedin FIG. 30.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter withreference to specific embodiments of the invention and particularly tothe various drawings provided herewith. Indeed, the invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. As used in the specification, and in the appended claims,the singular forms “a”, “an”, “the”, include plural referents unless thecontext clearly dictates otherwise.

The invention comprises high strength micro- and nanofiber nonwoven websprepared in a spunbond process. The nonwoven, spunbonded webs areprepared from multicomponent fibers, such as islands in the sea (I/S)fibers. The materials prepared according to the invention can becustomized to have defined characteristics through varying the types ofpolymers used in preparing the fibers, varying the number and averagediameter of the islands present in the multicomponent fibers, andvarying other production parameters that can affect fiber mechanicalproperties.

In the fiber industry, there is no commonly accepted definition ofnanofibers. Some authors refer to them as materials with a diameterranging from 0.1 to 0.5 μm (100-500 nm), while others consider filamentssmaller than 1 μm (1000 nm) to be nanofibers. Still others describenanofibers as fibers with diameters below 0.1 μm (e.g., 100 nm). As usedherein, the term “nanofibers” refers to a fiber having an averagediameter of about 500 nm or less. The term “microfiber”, as used herein,refers to a fiber having an average diameter ranging from about 0.5 μmto about 5 μm. Thus, collectively, the phrase “micro- and nanofibers”refers to fibers generally having diameters of about 5 μm or less, and“micro- and nanofibers” can indicate microfibers, nanofibers, or acombination of microfibers and nanofibers.

The present invention is characterized by the ability to easily andreliably prepare nonwoven spunbonded materials comprising micro- andnanofibers. Such materials provide benefit in a variety of arenasarising from useful properties of the microfibers and nanofibers, suchas relatively large surface area, small pore size, flexibility, andlightness. The nonwoven, spunbonded materials of the invention preparedusing micro- and nanofibers find use in numerous applications, such asliquid and air filters, barrier fabrics (e.g., medical gowns andfacemasks), tissue engineering, technical and personal care wipes, andartificial leather products.

There are methods known in the art for preparing microfibers andnanofibers; however, such known methods suffer from many drawbacks andare not useful for preparing spunbonded materials as described herein.For example, electrospinning allows for preparation of nanofibers bydrawing a fiber from a polymer solution using electrostatic forces.Electrospinning is disadvantageous, though, because it is difficult toprepare a single, continuous fiber by this method (rather nonwoven websare generally unavoidable). Moreover, it is difficult to control fiberdiameter and molecular orientation, the spun webs exhibit poormechanical properties, the method is generally limited to the use of lowviscosity polymers, vapor production raises environmental issues, properprocedures must be followed to avoid fiber inhalations, andelectrospinning is typically plagued by low productivity.

The present invention overcomes these problems by providing methods ofpreparing spunbonded fabrics comprising multicomponent fibers.Accordingly, in one embodiment, the method of the invention comprisesextruding continuous filament multicomponent fibers and mechanicallyentangling the multicomponent fibers to form a nonwoven spunbondedfabric. The multicomponent fibers preferably have a predeterminedaverage diameter and have an islands in the sea configuration comprisinga plurality of island components comprising a first polymer surroundedby a sea component comprising a second polymer.

A typical apparatus for preparation of a spunbonded material usingmulticomponent fibers is illustrated in FIG. 1, wherein an extruderapparatus 100 and a web-forming apparatus 200 are generally shown. Anyapparatus useful for extruding polymeric materials into fibers,particularly multicomponent fibers, could be used as an extruderapparatus according to the inventive method, which is not limited to thespecific embodiment illustrated in FIG. 1. Likewise, any apparatususeful for collecting extruded fibers to form a web, particularly anonwoven web, could be used as a web-forming apparatus according to theinventive method, which is not limited to the specific embodimentillustrated in FIG. 1.

As seen in FIG. 1, the extruder apparatus 100 is set up for forming abicomponent fiber from a first polymer and a second polymer and thuscomprises first and second extruder drives 105, 106 and first and secondpolymer hoppers 110, 111, which feed the polymers through a filter 115and into a melt pump 120. The polymers move through a spinneret 125which preferably includes a die (not shown) for forming a desired numberof multicomponent fibers having the appropriate multicomponentstructure. Extrusion processes and equipment, including spinnerets, formaking multicomponent continuous filament fibers are well known and neednot be described here in detail. Generally, a spinneret includes ahousing containing a spin pack which includes a plurality of platesstacked one on top of the other with a pattern of openings arranged tocreate flow paths for directing fiber-forming components separatelythrough the spinneret. The spinneret has openings or holes arranged inspecified patterns. The polymers are combined in a spinneret hole. Thespinneret is configured so that the extrudant has the desired overallfiber cross section (e.g., round, trilobal, etc.). The spinneretopenings form a downwardly extending curtain of filaments. Such aprocess and apparatus is described, for example, in U.S. Pat. No.5,162,074, to Hills, which is incorporated herein by reference.

Following extrusion through the die, the resulting thin fluid strands,or filaments, remain molten for some distance before they are solidifiedby cooling in a surrounding fluid medium, which may be chilled air blownthrough the strands. As illustrated in FIG. 1, the extruded fibers aresolidified using an air quencher 130. The quenched fibers are gatheredand oriented using an air attenuator 135 following extrusion through thedie and then directed onto the web-forming apparatus 200.

The web-forming apparatus 200 typically comprises a take-up surface,such as a roller or a moving belt. In FIG. 1, the take-up surfacecomprises a forming belt 205, which can be perforated. The forming beltmoves around a series of guide rollers 210 in the direction of thearrows shown parallel to the belt. The web-forming apparatus furthercomprises an edge guide 215 to maintain the forming belt 205 on theguide rollers 210 and assist with formation of a uniform web. In thisway, a spunbond web is formed on the belt. Such forming can also includethe use of forced air to direct the fibers onto the belt.

FIG. 1 further illustrates an optional compaction roller 220, which canbe used to compress the formed web. A calendar 230 is also illustratedand can be optionally present to thermally bond the nonwoven web. Inknown spunbonding methods, the use of a calendaring device is necessaryto ensure the strength and integrity of the spunbonded material bythermally bonding multiple portions of the nonwoven fibers; however, thepresent invention makes the use of such thermal bonding equipment solelyoptional. The formed nonwoven spunbonded material 500 can be rolled ontoa winder 240 to collect the finished material. Other process steps notillustrated in FIG. 1 can also be included according to the invention.For example, prior to moving onto the winder 240, the spunbondedmaterial 500 can be directed through an appropriate apparatus formechanically binding the spunbonded material 500, as further describedbelow. In this manner, the present invention allows for the use ofcontinuous filaments to form a nonwoven, spunbonded material, which isfavorable because it provides for good fiber orientation andcrystallinity, high strength, and low fiber diameter variability.

As previously pointed out, the multicomponent fibers of the presentinvention preferably have an islands in the sea (I/S) configuration. Oneembodiment of an I/S multicomponent fiber useful according to theinvention is shown in FIG. 2. Only a segment of the multicomponent fiberis shown in FIG. 2, but the fiber illustrates both a cross-section ofthe multicomponent fibers as well as a cut-out section of the fiber. Thefiber 300 comprises a sea component 310 and a plurality of islandcomponents 320 surrounded by the sea component 310. The fiber 300 alsocomprises an outer surface 330 that generally comprises the sea-formingpolymer.

In cross-section, the I/S fiber can be seen to have a discrete diameter.The method of the invention is particularly beneficial in that nonwovenmaterials can be prepared using fibers having diameters that aresubstantially continuous along the length of the multicomponent fiber.The diameter of the multicomponent fiber is further important, as morefully discussed below, because most known methods of preparing nonwovenmaterials are limited by the overall diameter of the fiber used. Forexample, in using segmented fibers, the average size of the segments isat least partially limited by the diameter of the multicomponent fiber.In the present invention, however, it is possible to maintain a uniformmulticomponent fiber diameter and reduce the average diameter of thefibers ultimately used to prepare the nonwoven material by increasingthe number of islands present in the multicomponent fiber.

Preferably, the multicomponent fiber prepared according to the inventivemethod has an average diameter in the range of about 5 μm to about 25μm. In further embodiments, the multicomponent fiber is extruded to havean average diameter in the range of about 5 μm to about 20 μm, about 5μm to about 15 μm, about 10 μm to about 20 μm, or about 10 μm to about15 μm. The present invention also encompasses multicomponent fibershaving smaller overall diameters, and the invention is only limited bythe capacity of the overall extrusion process. For example, it ispossible to prepare multicomponent fibers having an overall diameter ofless than 5 μm and still incorporate a plurality of island componentswithin a sea component according to the present invention.

The method of the present invention is preferably not limited to aspecific type of polymer used in preparing the sea component or theisland components. Rather, various types of polymer can be used foreither component according to the invention. It is possible to use thesame type of polymer for both the sea component and the islandcomponents. For example, the same polymer type could be used for bothcomponents, but certain properties of the polymers be varied, such asmolecular weight. Likewise, one component could comprise substantially afirst polymer and the other component could comprise a copolymer orterpolymer comprising the first polymer and one or more furtherpolymers.

In preferred embodiments, the polymer used in preparing the seacomponent is different from the polymer used in preparing the islandcomponents. This allows for easy removal of the sea polymer withoutdisturbing the island components or disturbing the integrity of theisland components. For example, it is useful for the sea component tocomprise a polymer that is easily removable, such as by washing orchemical treatment. Accordingly, it is useful for the island componentsto comprise a polymer that is substantially resistant to the treatmentused to remove the sea component. Preferentially, the sea componentcomprises a polymer that is water soluble or water dispersible. Infurther embodiments, the sea polymer can be recyclable or biodegradable.

The polymer used in preparing the sea component can be referred to asthe “fugitive” polymer component and can comprise any polymer capable ofbeing removed by washing or other treatment. Preferably, the sea formingpolymer comprises a synthetic melt-processable polymer substantiallysoluble in a benign solvent, such as water, an aqueous caustic solution,or a non-halogenated organic solvent. Non-limiting examples of polymerscapable of being dissolved in water include sulfonated polyesters (e.g.,sulfonated polyethylene terephthalate), sulfonated polystyrene, andcopolymers or polymer blends containing such polymers (e.g., Eastman AQ55S), ethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH),polyethylene oxide, and copolymers or polymer blends containing suchpolymers. Non-limiting examples of polymers that are substantiallysoluble in aqueous caustic solution include polyglycolic acid (PGA),poly(lactic) acid (PLA), polycaprolactone (PCL), and copolymers orblends thereof. The term “poly(lactic) acid” is intended to encompasspolymers that are prepared by the polymerization of either lactic acidor lactide. Reference is made to U.S. Pat. Nos. 5,698,322; 5,142,023;5,760,144; 5,593,778; 5,807,973; and 5,010,145, the entire disclosure ofeach of which is hereby incorporated by reference. Other examples ofpolymers useful as the sea component include copolymers of polyethyleneterephthalate (PET), which are referred to as “co-PET”, that are solublein aqueous media, such as. An example of a polymer that is substantiallysoluble in one or more non-halogenated organic solvents, such as hexaneor xylene, is polystyrene.

Generally, any type of polymer recognized as capable of extrusion can beused according to the invention. For example, any polymer capable offorming a multicomponent fiber (e.g., a polymer capable of formingisland components or a polymer capable of forming a sea component) canbe used according to the invention. Preferably, if the nonwovenspunbonded material being prepared is intended for use in a specificenvironment requiring certain polymer properties, the island componentscan comprise a polymer providing the desired properties. In preferredembodiments, polymers useful in preparing the island componentsaccording to the invention include polyolefins (e.g., polyethylene andpolypropylene), polyamides (e.g., nylon and nylon-6), polyesters (e.g.,polyethylene terephthalate (PET) and polybutylene terephthalate (PBT)),thermoplastics (e.g., thermoplastic polyurethane (TPU)), and the like.

The method of the invention is particularly useful in the preparation ofmaterials having superior properties because of the specific spinpackdesign used in extruding the multicomponent fibers. In known methods ofpreparing I/S fibers it is common for a portion of the island componentsto not be completely surrounded by the sea component (i.e., portions ofthe island components protrude through the sea and are in direct contactwith the ambient environment). FIG. 3 provides a scanning electronmicrograph (SEM) image of an I/S multicomponent fiber prepared accordingto known techniques. As seen therein, the island components are formedin a distinct pattern within the sea component, and the outermost islandcomponents are in physical connection with, and form part of, the outersurface of the multicomponent fiber. The present invention, however,specifically avoids such a design.

As seen in FIG. 2, the multicomponent fiber of the present invention isprepared to comprise an outer surface 330 that is formed of the seaforming polymer. Moreover, the sea component 310 completely surroundsthe island components 320 such that none of the island components formany portion of the outer surface 330 of the multicomponent fiber 300.Preferably, the sea component 310 completely surrounds the islandcomponents 320 such that the sea component 310 forms a sheath 340 aroundthe island components 320. The sheath 340 is preferably a continuouslayer of the sea forming polymer around the circumference of themulticomponent fiber. An SEM image showing multicomponent fibersprepared according to the present invention is provided in FIG. 4. Asseen therein, the island components are completely surrounded by the seacomponent such that the sea component forms a sheath around the islandcomponents.

The sheath can be defined as having a thickness that is measured betweenthe outer surface of the multicomponent fiber and the outer edge of theislands nearest the outer surface of the multicomponent fiber. Theaverage thickness of the sheath can vary, but the thickness ispreferentially sufficient to completely wrap the islands within the seaand be capable of functioning as a protective shield during fiberspinning. In a particularly preferred embodiment, the sheath has athickness that is greater than or equal to the average diameter of theisland components within the particular multicomponent fiber. Forexample, in a multicomponent fiber comprising a plurality of islandshaving an average diameter of 500 μm, the sea forming polymer sheathsurrounding the islands has a thickness of at least 500 μm.

The specifically defined sheath portion is particularly useful forovercoming multiple challenges to spinning high quality fibers. Forexample, the presence of the sheath can assist in avoiding prematuresolidification of the island components. This is beneficial in that thefibers can be properly drawn and attenuated while the islands are in asufficiently molten state so that mechanical properties of the islandcomponents are not compromised. Moreover, the sheath can also overcomehandling problems associated with relatively small extruded fibers. Forexample, many types of materials used in fiber preparation, such aspolyamides, are plagued by static electricity problems, which makehandling of the fibers particularly difficult. To overcome this problem,it is common in the art to use anti-static additives with the polymersfor extrusion. According to the present invention, however, suchadditives are not necessary. Rather, it is possible to use a polymer forthe sea component that does not have associated static electricityproblems, regardless of the type of polymer used for the islandcomponents. Since the non static forming polymer is completelysurrounding the static forming islands, there is no perceived inductionof static charge associated with the extruded fibers, and anti-staticadditives can be completely avoided.

The fibers used in preparing the nonwoven spunbonded materials of thepresent invention also exhibit further beneficial properties. Forexample, preparing the I/S multicomponent fiber such that the seacomponent forms a sheath completely surrounding the island componentsprovides for improved crystalline orientation of island components andthe sea component. While not wishing to be bound by theory, it isbelieved that the island components solidify faster according to thepresent invention than the sea component or fibers prepared comprising100% by weight of the polymer used in the island components. Thus, theisland components experience higher spin-line stresses than the seacomponent and develop better molecular orientation. Moreover, the islandcomponents tend to reach final fiber spinning speed faster than the seacomponent of the I/S fiber. Accordingly, the presence of the islandcomponents can promote attenuation of the sea component as the result ofthe shearing forces acting on the interface between the components. Thiscan at least partially account for an observed improvement of thecrystalline orientation of the sea component polymer compared tohomopolymer fibers prepared using the same polymer component.

As previously noted, prior art methods for preparing spunbondedmaterials requires the use of thermal bonding to provide strength andintegrity to the spunbonded fibers. This is because the fibers aregenerally laid on a support in overlapping fashion and the formed webcan be easily disrupted by pulling apart the fibers. Thermal bonding ofthe fibers at multiple points physically interconnects the overlappingfibers so that they cannot easily be torn apart. In the preparation ofmaterials from micro- and nanofibers from I/S multicomponent fibers,though, it is a usual practice to remove the sea component to leave theislands as micro- and nanofibers. Removal of the sea, however, alsogenerally removes the bonds formed during the thermal bonding step.Moreover, any remaining bonds are susceptible to disintegration duringfurther downstream processing of the material. Thus, the remainingfibers are again free to be easily disrupted, which means the integrityof the material is totally compromised by the step of removing the seacomponent.

In the present invention, thermal bonding can be totally avoided or onlyoptionally used. Instead, the present invention provides strength andintegrity to the nonwoven spunbonded materials by mechanicallyentangling the multicomponent fibers. Any method recognized as useful inthe art can be used to mechanically entangle the nonwoven spunbondedmaterial prepared according to the invention. Preferably, the entanglingmethod provides sufficient mechanical energy to entangle themulticomponent fibers to an extent wherein fibers become mechanicallybonded and are imparted an inherent strength. Non-limiting examples ofmechanical entangling methods useful according to the present inventioninclude hydroentangling, needle punching, and steam jet entangling. Ofcourse, combinations of such methods, as well the use of other methods,are fully encompassed by the present invention.

One embodiment of a method for hydroentangling a nonwoven spunbondedmaterial prepared according to the present invention is illustrated inFIG. 5. As seen therein a nonwoven web 500 enters the hydroentanglingprocess and sequentially rolls partially around a first drum 420 andthen a second drum 425. While in contact with the first drum 420, theweb 500 is subject to pressurized water jets 435 provided by one or moremanifolds 430. The water pressure provided can be increased or decreasedas desired to increase or decrease the extent of hydroentangling, asdesired. Accordingly, the mechanically entangling step of the inventiveprocess can be referred to in terms of high energy entangling or lowenergy entangling. As would be understood by the skilled person, highenergy entangling can be used to increase the extent of entangling andcan be particularly needed when entangling a web of relatively highweight. Low energy entangling can be preferred with relatively lowweight webs and can be beneficial for reducing the overall energy costsassociated with the process.

The terms “high energy entangling” and “low energy entangling” candepend upon specific variables in the fabric manufacturing process. Forexample, the basis weight of the fabric can affect what is low energyversus high energy (e.g., what is considered high energy for a fabric ofa given basis weight could be considered low energy for a fabric havinga significantly greater basis weight). Likewise, entangling energy canalso be relative to the speed of the overall process. In one embodimentlow energy entangling of a 200 g/m² web prepared at a speed of 10 metersper minute is in the range of about 1,000 kJ/kg of fabric to about 3,000kJ/kg of fabric. For a web of the same basis weight prepared at the samespeed, high energy entangling is in the range of about 6,000 kJ/kg offabric to about 8,000 kJ/kg of fabric. Similar values for fabrics of adiffering basis weight could be easily determined by the skilled personin light of the further disclosure provided herein.

As seen in FIG. 5, the nonwoven web 500 comprises a first surface and anopposing surface. After leaving the second drum 425, the web 500 passesaround an optional aligning roller 440 and can proceed for furtherprocessing. In FIG. 5, water jets 435 are illustrated in relation toboth the first drum 420 and the second drum 425. Accordingly, it ispossible to provide mechanical entangling to both surfaces of thenonwoven web 500. Of course, the invention also encompasses embodimentswherein mechanical entangling is only provided to only one surface ofthe nonwoven web. Moreover, it is possible according to the invention toprovide high energy entangling to a first surface of the web and lowenergy entangling to an opposing surface of the web. Still further, itis possible to only provide a single position for provision ofentangling energy (i.e., one drum and a single manifold or a single setof manifolds). The nonwoven web is generally described herein as havinga “first surface” and an “opposing surface” for ease of description anddoes not necessarily limit the nonwoven spunbonded web. In preferredembodiments, the surfaces of the web are generally indistinct. Ofcourse, it is possible to specifically treat or process the web suchthat the two surfaces are distinct and have separate properties, and thepresent invention also encompasses such embodiments.

Entangling of the web is preferably carried out to a point such that thematerial prepared thereby can withstand subsequent processing of theweb, such as removal of the sea component of the multicomponent fiber.For example, the fibers in the material are preferably entangled to adegree that the fibers will substantially avoid protruding from thesurface of the material causing a condition known as “fuzz”.

The method of the invention can further comprise removal of the seacomponent of the multicomponent fibers forming the nonwoven spunbondedmaterial. Any method known in the art for removing a sea component in anI/S fiber can be used. In particular, the method of removing the sea canbe specifically associated with the polymer used in preparing the seacomponent. For example, in embodiments wherein the sea forming polymeris water soluble or water dispersible, the method of removing the seacomponent can comprise subjecting the nonwoven spunbonded material towater treatment. Similarly, in embodiments wherein the sea formingpolymer is subject to chemical dissolution or dispersion, the method ofremoving the sea component can comprise subjecting the nonwovenspunbonded material to a specific chemical treatment. Of course, furthermethods for removing a sea component in an I/S multicomponent fiber canbe used according to the present invention.

In one specific embodiment, the sea component is removed by passing thespunbonded fabric through a winch beck machine, which generallycomprises a bath and a winch component for moving the fabric through thebath. Winch beck machines are known in the art and are commonly used fordyeing textiles. In a winch beck machine, the winch draws the fabric viaa guide roller out of the bath and returns it in folds into the bath. Inthe conventional winch beck, the bath stands still, while the fabric iskept in circulation by a reel positioned in the upper part of themachine. In modern winches both the bath and the fabric are kept incirculation, which improves homogenization and exchange of the liquorwith the fabric.

In embodiments where the sea component is subject to removal throughcontact with water or an aqueous solution, any method for causingsignificant contact of the fibers of the material with the aqueouscomponent for removal of the sea component could be used according tothe invention. For example, conventional jet dyeing processes could beused, as well as jet steam removal processes. Generally, any methodscapable of wetting the fabric with the aqueous component and maintainingcontact of the aqueous component with the fabric fibers for a timesufficient to allow the solvent to remove the sea component can be used.Preferably, such methods are followed by a wash stage to remove thedissolved sea component and any residual reactants.

As previously noted, the sea component can be removed using a variety ofmethods and reactants. Generally, where a reactant is used to remove thesea component, such removal can be carried out by contacting the fiberswith the reactant for a time sufficient to at least partially remove thesea component. For example, in embodiments where organic materials inthe liquid state are used, the fibers could be subjected to methods suchas described above for sea removal. Alternate methods, such as placingthe fibers in a vapor chamber, could also be used and would be apparentto the skilled person with the benefit of the present disclosure andknowledge of the physical characteristics of the sea component.

The nonwoven spunbonded materials prepared according to the presentinvention are particularly useful in that the multicomponent fibers canbe treated to remove the sea component and leave behind a materialcomprising micro- and nanofibers without compromising the integrity ofthe material. An SEM image showing a multicomponent fiber according toone embodiment of the invention having the sea component partiallyremoved to reveal the individual island components is illustrated inFIG. 6.

Since the multicomponent fibers are mechanically entangled as describedabove, the island components present within the multicomponent fibersremain entangled after removal of the sea component. The remainingmaterial is a nonwoven spunbonded web formed of micro- and nanofibers.In certain embodiments, thermal bonding can be combined with themechanical entangling methods. Such thermal bonding can be used beforeor after removal of the sea component. Of course, it is recognized thatwhile thermal bonding can add strength to the nonwoven spunbondedmaterial prepared according to the present invention, the use of thermalbonding is purely optional. For example, the use of thermal bondingafter removal of the sea component has been shown to provide mildincreases in tensile strength, likely arising from an increasedstiffness; however, such thermal bonding has also been shown to decreasethe tear strength of a hydroentangled web prepared according to theinvention. Accordingly, in relation to mechanical properties, theusefulness of thermal bonding is limited. Thermal bonding after removalof the sea component, though, can be useful for improving pilling andabrasion resistance of the prepared material. For example, calendaringof a material typically ties down the fibers on the fabric surface, andthis in turn increases resistance to pilling (or formation of fabricpills on the surface of the fabric), as well as abrasion resistance.

The method of the invention allows for the preparation of high strengthmaterials comprising micro- and nanofibers through spunbonding ofmulticomponent fibers. In specific embodiments, the fibers comprise I/Sfibers, and the sea component is removed to leave behind micro- andnanofibers. The resulting size of the fibers (e.g., micro, nano, ormicro and nano) can depend upon a variety of factors. Generally, if thenumber of islands remains constant, a multicomponent fiber with asmaller average diameter will produce islands having smaller averagediameters and a multicomponent fiber having a larger average diameter.Moreover, if the average diameter of the multicomponent fiber remainsconstant, a multicomponent fiber with a greater number of islands willproduce islands having smaller average diameters that a multicomponentfiber with a lesser number of islands. Island diameter is also relatedto the ratio of the sea component to the island components. As the ratioof sea component increases, the average diameter of the islandsdecreases.

The above conditions are supported by both theoretical calculations andactual experimental data. The relationship between the average diameterof the multicomponent fiber, the number of islands present in themulticomponent fiber, and the average diameter of the islands within themulticomponent fiber is illustrated in FIG. 7 and FIG. 8. In FIG. 7,theoretical calculations for multicomponent fibers having the followingcomposition are provided: 75/25 islands/sea ratio and an averagemulticomponent fiber diameter of 10 μm; and 75/25 islands/sea ratio andan average multicomponent fiber diameter of 20 μm. Experimental data isshown for a multicomponent fiber with a 75/25 islands/sea ratio and anaverage diameter of 16-18 μm (wherein the islands comprise polypropyleneand the sea comprises polyethylene). As seen in FIG. 7, the averagediameter of the islands decreases with an increase in the number ofislands present in a given multicomponent fiber. In FIG. 8, thetheoretical data is the same, and the experimental data is shown for amulticomponent fiber with a 75/25 islands/sea ratio and an averagediameter of 14-16 μm (wherein the islands comprise nylon-6 and the seacomprises poly(lactic) acid (PLA)). Again, the average diameter of theislands decreases with an increase in the number of islands present in agiven multicomponent fiber. This is further illustrated in the Examplesbelow.

As evident from the description provided herein, the properties of thenonwoven spunbonded material prepared according to the present inventioncan be at least partially determined by the properties of themulticomponent fiber extruded to form the spunbonded web. Moreover, thedesired properties of the nonwoven spunbonded material can be achievedby optimizing multiple fiber dimensions and properties. For example, byextruding a multicomponent fiber having a specified average diameter,specified number of islands, and specified island to sea ratio, anonwoven spunbonded fabric can be prepared having specific mechanicaland physical properties, as further described below.

Accordingly, the method of the present invention can be furtherdescribed in terms of the specific properties of the extruded fibers.Preferentially, the invention comprises the preparation of materialsincorporating micro- and nano fibers, and such micro- and nano fiberscan be provided initially as island components in an I/S multicomponentfiber that are released by removal of the sea component of the fiber.Accordingly, the invention encompasses the use of micro- and nanofibershaving an average diameter of about 5 μm or less.

In certain embodiments, it is preferred for the step of extruding themulticomponent fibers to comprise forming a multicomponent fibercomprising island components having an average diameter in the range ofabout 50 nm to about 5 μm. In further embodiments, the multicomponentfiber is extruded to form a multicomponent fiber comprising islandshaving an average diameter in the range of about 50 nm to about 3 μm,about 50 nm to about 2 μm, about 50 nm to about 1 μm, about 100 nm toabout 1 μm, about 100 nm to about 800 nm, about 200 nm to about 800 nm,or about 300 nm to about 800 nm.

The multicomponent fiber prepared in the method of the present inventioncan also be extruded so that the multicomponent fiber comprises adefined number of island components. Preferably, the multicomponentfiber comprises up to about 1000 island components. In furtherembodiments, the multicomponent fiber comprises between about 2 andabout 1000 island components, between about 36 and about 1000 islandcomponents, between about 36 and about 800 island components, betweenabout 36 and about 600 island components, or between about 36 and about400 island components. SEM images showing various embodiments ofmulticomponent fibers prepared according to the invention areillustrated in FIG. 4 (cross-section of a multicomponent fiber having 18island components), FIG. 9, (cross-section of a multicomponent fiberhaving 36 island components), FIG. 10, (cross-section of amulticomponent fiber having 108 island components), FIG. 11,(cross-section of a multicomponent fiber having 216 island components),and FIG. 12 (cross-section of a multicomponent fiber having 360 islandcomponents).

In yet further embodiments, the multicomponent fiber can be extruded sothat the multicomponent fiber comprises a defined ratio of islandcomponent to sea component (i.e., an “island/sea ratio”). Preferably,the fiber is extruded such that the multicomponent fiber comprises agreater proportion of the island component than the sea component. Inparticular embodiments, the fiber is extruded such that themulticomponent fiber comprises an island/sea ratio in the range of about95/5 to about 5/95, about 85/15 to about 15/85, or about 75/25 to about25/75.

The relationship between average multicomponent fiber diameter, I/Sratio, the number of islands present in the multicomponent and theaverage diameter of the island components after removal of the sea canbe calculated according to Formula (1) provided below

$\begin{matrix}{d_{isl} = {\sqrt{\frac{R_{isl}}{N}}D_{f}}} & (1)\end{matrix}$

wherein d_(isl) is the diameter of the island fibers after dissolving ofthe sea component, N is the number of island components present in themulticomponent fiber, R_(isl) is the ratio of island components to seacomponent, and D_(f) is the diameter of the multicomponent fiber beforeremoval of the sea component. Various I/S multicomponent fiberembodiments possible according to the invention and illustrating theinfluence of island count and I/S rations on the average diameter of theisland component are shown below in Table 1.

TABLE 1 Initial Multicomponent Fiber Diameter Initial MulticomponentFiber Diameter (Df) = 10 μm (Df) = 20 μm Number Island ComponentDiameter (d_(isl)) After Island Component Diameter (d_(isl)) After ofRemoval of Sea Component (μm) Removal of Sea Component (μm) IslandsIsland/Sea Ratio Island/Sea Ratio (N) 25/75 50/50 75/25 25/75 50/5075/25 36 0.83 1.18 1.44 1.67 2.36 2.89 72 0.59 0.83 1.02 1.18 1.67 2.04108 0.48 0.68 0.83 0.96 1.36 1.67 144 0.42 0.59 0.72 0.83 1.18 1.44 1800.37 0.53 0.64 0.74 1.05 1.29 216 0.34 0.48 0.59 0.68 0.96 1.17 252 0.310.44 0.54 0.63 0.89 1.09 288 0.29 0.42 0.51 0.59 0.83 1.02 324 0.28 0.390.48 0.55 0.79 0.96 360 0.26 0.37 0.46 0.53 0.74 0.91 600 0.20 0.29 0.350.41 0.58 0.71 1000 0.16 0.22 0.27 0.32 0.45 0.55

The methods of the present invention allow for the preparation ofnonwoven spunbonded materials comprising micro- and nanofibers. This isparticularly useful in that such materials can be lightweight whilestill providing excellent mechanical properties, such as high strength.The nonwoven spunbonded materials of the present invention exhibit highstrength in both the machine direction (MD) (i.e., the direction inwhich the extruded fibers were laid on the moving belt) and the crossmachine direction (CD). The strength of the nonwoven spunbonded materialcan particularly be evaluated in terms of tensile strength and tearstrength. As would be recognizable by the skilled person, suchproperties in relation to a nonwoven material can change depending uponthe overall web weight (i.e., the mass of the web per given area). Toestablish a standardized basis, the tear strength and tensile strengthvalues provided for the nonwoven spunbonded materials prepared accordingto the present invention are provided on a basis weight of 100 g/m²(herein referred to as “the normalized basis”).

While not intending to be so limited, the values provided herein forvarious mechanical and physical properties are particularly seen inmaterials prepared using micro- and nanofibers formed of a polyamide(e.g., nylon-6). In other words, the fibers are left after removal ofthe sea component of a multicomponent fiber formed comprising polyamideisland components. Of course, the values provided herein are alsorelative to other polymer types and are not necessarily intended to belimited to polyamides.

One of skill in the art would readily be capable of making ahead-to-head evaluation of the mechanical properties of the nonwovenspunbonded materials prepared according to the present invention againstmaterials made by other methods and possibly having a different basisweight. Such is easily achieved by converting to a normalized basisweight using Formula (2) provided below

P _(N) =P _(O)·(B _(n) /B _(o))  (2)

wherein P_(N) is the normalized property being evaluated, P_(o) is theobserved property value, B_(n) is the chosen nominal basis weight, andB_(o) is the observed basis weight of the material being evaluated.

In preferred embodiments, the nonwoven spunbonded materials preparedaccording to the method of the present invention (including removal ofthe sea component) have a normalized MD tensile strength of at leastabout 25 N. In further embodiments, the nonwoven spunbonded materialshave a normalized MD tensile strength of at least about 50 N, at leastabout 100 N, at least about 150 N, at least about 200 N, at least about250 N, or at least about 300 N. In other embodiments, the nonwovenspunbonded materials have a normalized CD tensile strength of at leastabout 25 N, at least about 50 N, at least about 100 N, or at least about125 N. The above values are provided on a 100 g/m² normalized basis.

The nonwoven spunbonded materials prepared according to the method ofthe present invention can further be characterized in terms of theirtear strength. In preferred embodiments, the nonwoven spunbondedmaterials have a normalized MD tear strength of at least about 25 N. Infurther embodiments, the nonwoven spunbonded materials have a normalizedMD tear strength of at least about 50 N, at least about 75 N, at leastabout 100 N, or at least about 125 N. In other embodiments, the nonwovenspunbonded materials have a normalized CD tear strength of at leastabout 50 N, at least about 75 N, at least about 100 N, at least about125 N, at least about 150 N, or at least about 175 N. The above valuesare provided on a 100 g/m² normalized basis.

The nonwoven spunbonded materials prepared according to the presentinvention also exhibit excellent physical properties, such as absorbentcapacity, absorbency rate, and air permeability. Absorbent capacitygenerally describes the ability of the material to absorb liquid intothe fibers and can be referred to as capillary absorption, which isgenerally determined by the size of the capillaries in the material.Absorbent capacity can be calculated based on the volume of liquidabsorbed by a given weight of dry fabric. Absorbency rate is determinedby the size and orientation of capillaries in the fabric, as well assurface properties of the fabric and the individual fibers and liquidproperties of the liquid being absorbed. Absorbency rate can becalculated as the volume of liquid absorbed by a given weight of dryfabric over a given time.

As illustrated in FIG. 13 and FIG. 14, absorbent capacity and absorbencyrate for fabrics prepared according to certain embodiments of theinvention tends to decrease as the number of islands used to prepare themulticomponent fibers increases. Such change generally arises from anoverall increase in the bulk density of the nonwoven spunbonded fabricwhen using a greater number of islands in the multicomponent fibers.Preferably, the nonwoven spunbonded materials prepared according to thepresent invention exhibit an absorbent capacity of at least about 5cm³/g. In further embodiments, the nonwoven spunbonded materials exhibitan absorbent capacity of at least about 7 cm³/g, at least about 10cm³/g, or at least about 12 cm³/g. Moreover, the nonwoven spunbondedmaterials prepared according to the present invention preferentiallyexhibit an absorbency rate of at least about 0.025 cm³/g·s. In furtherembodiments, the nonwoven spunbonded materials exhibit an absorbencyrate of at least about 0.05 cm³/g·s, at least about 0.1 cm³/g·s, atleast about 0.15 cm³/g·s, at least about 0.2 cm³/g·s, at least about0.25 cm³/g·s, or at least about 0.3 cm³/g·s.

Air permeability of the inventive materials can also vary with thenumber of islands present in the extruded multicomponent fibers. Suchchange is illustrated in FIG. 15. Air permeability can be calculated asthe volume of air per second passing through a defined area of fabric.Preferably, the nonwoven spunbonded material prepared according to thepresent invention exhibits an air permeability of at least about 5(cm³/s)/cm². In further embodiments, the nonwoven spunbonded materialexhibits an air permeability of at least about 10 (cm³/s)/cm², at leastabout 25 (cm³/s)/cm², at least about 50 (cm³/s)/cm², at least about 75(cm³/s)/cm², or at least about 90 (cm³/s)/cm².

EXPERIMENTAL

The present invention will now be described with specific reference tovarious examples. The following examples are not intended to be limitingof the invention and are rather provided as exemplary embodiments.

Example 1 Preparation of Spunbond Web Using Bicomponent Fibers

Bicomponent I/S fibers were prepared using ULTRAMID® BS 700 nylon-6polymer (available from BASF) as the island components and PLA as thesea polymer. Polymer properties are provided below in Table 2. Thebicomponent fibers were prepared to have 36, 108, 216, or 360 islandcomponents using standard spinning methods as described herein andcontinuously laid on a forming belt to form a nonwoven web. The nonwovenweb was hydroentangled at a speed of 30 m/min to form a nonwovenspunbonded fabric. The total hydroentangling energy used was 8000 kJ/kg.The basis weight of the fabric was maintained at 170 g/m² for allsamples. A description of the samples prepared is provided below inTable 3.

The PLA sea was removed in a winch beck machine by treating the fabricfor 10 minutes in a 3% solution of caustic soda in water at atemperature of 100° C. The basis weight of the fabric after removal of25% of the PLA sea was 140 g/m². The basis weight of the fabric afterremoval of 75% of the PLA sea was 50 g/m².

TABLE 2 Polymer Melt Temp. Density Viscosity Nylon-6 220° C. 1.14 g/cm³2.67-2.73 PLA 173° C. 1.25 g/cm³ NA

TABLE 3 Sea Island Sample Polymer Polymer No. of Islands Island/SeaRatio 1 Nylon-6 NA NA  0/100 2 PLA NA NA  0/100 3 PLA Nylon-6 36 25/75 4PLA Nylon-6 36 75/25 5 PLA Nylon-6 108 25/75 6 PLA Nylon-6 108 75/25 7PLA Nylon-6 216 25/75 8 PLA Nylon-6 216 75/25 9 PLA Nylon-6 360 25/75 10PLA Nylon-6 360 75/25

Example 2 Crystallinity and Crystalline Orientation

Wide-angle X-ray scattering (WAXS) profiles of the fibers prepared inExample 1 were obtained by Omni Instrumental X-ray diffractometer with aBe-filtered CuKα radiation source (λ=1.54 Å) generated at 30 kV and 20mA. The I/S fibers were manually wound in a tightly packed flat layer ofparallel fibers onto a holder prior to the examination. The samples wereequatorially scanned at the rate 0.2° min⁻¹ from 2θ=10°−35° in thereflection geometry for a count time of 2.5 seconds. Intensity curves ofthe equatorial scans were resolved into peaks at 20=22° for nylon-6fibers and at 20=16.5° for PLA fibers. To calculate Herrman'sorientation functions, transmission scans of the samples at the rate of0.5° min⁻¹ and count time 1 second at fixed diffraction angles wereperformed.

The relationships between the number of islands and crystallinity of thenylon-6 and PLA phases in the I/S fibers are illustrated in FIG. 16 aand FIG. 16 b, respectively. Bicomponent fibers made up of 36 islandsshowed the highest crystallinity for the nylon-6 component, whichdecreased slightly as the number of islands increased from 36 to 360.The fibers with 360 islands exhibited the highest degree ofcrystallinity for the PLA phase. Overall, the crystallinities of bothcomponents of the I/S fibers were lower than the crystallinities of purenylon-6 and PLA fibers.

The Herrman's orientation functions for the nylon-6 and PLA phases ofthe I/S fibers as functions of the number of islands are illustrated inFIG. 17 a and FIG. 17 b, respectively. This value describes theorientation of the polymer chains in relation to the fiber axis, whereina value of 1 indicates perfect orientation of the polymer chains alongthe fiber axis, and a value of −0.5 indicates perfect orientation of thepolymer chains perpendicular to the fiber axis.

The Herrman's orientation function of the nylon-6 component declined asthe number of islands increased from 36 to 216. Further increases in theisland count from 216 to 360 caused an increase in the crystallineorientation function of the nylon-6 phase. The 108 I/S fibersdemonstrated the lowest Hemnan's orientation function of the PLAcomponent, and this function increased as the number of islandscomposing the bicomponent fibers increased from 108 to 360. Fiberscontaining 36 islands demonstrated the highest values of the Herrman'sorientation functions for both phases. Overall, nylon-6 and PLAcomponents of the bicomponent fibers as well as 100% nylon-6 and PLAfibers showed low orientation of their polymer chains in the crystallineregions. However, the axial alignment of the component polymer chainswas found to be better than the alignment of the polymer chains of thehomo-component nylon-6 and PLA fibers along the fiber axis.

Example 3 Fiber Mechanical Properties Before and after PLA Sea Removal

Tenacity and initial modulus properties of the composite I/S fibersprepared according to Example 1 (without removing PLA) are illustratedin FIG. 18 and FIG. 19, respectively. With the exception of tenacity forthe filaments with 25% nylon-6, all fibers containing 360 islands showedthe highest tenacity and initial modulus. Overall, the I/S fibersdemonstrated performance similar to that of PLA homo-componentfilaments, which had a lower elongation to break than 100% nylon-6fibers. Thus, the I/S fibers tended to exhibit tensile propertiessimilar to those of 100% PLA fibers. The degree of entangling of themulticomponent fibers can be seen in FIG. 20 and FIG. 21. FIG. 20provides an SEM image of a hydroentangled fabric before removal of thesea component prepared according to the invention having 216 islandcomponents. FIG. 21 provides an SEM image of a hydroentangled fabricbefore removal of the sea component prepared according to the inventionhaving 360 island components.

Tenacity and initial modulus properties of the nylon-6 islands after theremoval of PLA from the nylon-6/PLA I/S fibers are illustrated in FIG.22 and FIG. 23, respectively. The data show that the values of the fibertenacity and initial modulus grew as the number of islands in theinitially prepared multicomponent fibers increased from 36 to 360. Themajority of the nylon-6 fibers exhibited performance superior to that ofthe I/S fibers. Overall, the nylon-6 fibers originally made up of 360islands showed the highest tenacity and modulus values. FIG. 24 and FIG.25 show the fabrics illustrated in FIG. 20 and FIG. 21, respectively,after removal of the sea component. As seen, the large number of micro-and nano-fibers provided by the freed island components provides for adensely entangled composition accounting for many of the improvedphysical and mechanical properties exhibited by the inventive fabrics.

Example 4 Fiber Diameter after Removal of PLA Sea

The diameters of the nylon-6 fibers (islands) after the removal of thesea were measured, and the results are provided below in Table 4 and aregraphically illustrated in FIG. 26. Average island diameter decreased asthe number of islands increased and as the ratio of the sea component tothe island components increased. The fibers with 25% nylon-6 showed adecrease in fiber diameter from 1.3 to 0.36 microns when the number ofislands was increased from 36 to 360. The diameter of fibers with 75%nylon-6 showed a decline from 2.3 to 0.5 micron for the same range. Theinitial diameter of the multicomponent fiber was 13 μm or 1.5 dpf(denier per filament).

TABLE 4 Number of Islands 75/25 I/S 50/50 I/S 25/75 I/S 36 2.26 μm 1.78μm 1.33 μm 108  1.2 μm  1.0 μm 0.77 μm 216 0.83 μm 0.67 μm 0.56 μm 3600.50 μm 0.48 μm 0.36 μm

Example 5 Fabric Mechanical Properties After PLA Sea Removal

Mechanical properties for the nylon-6 webs prepared according to Example1 after hydroentangling and removal of the PLA sea are illustrated inFIG. 27 a through FIG. 28 b. FIG. 27 a illustrates MD tensile strength;FIG. 27 b illustrates CD tensile strength; FIG. 28 a illustrates CD tearstrength; FIG. 28 b illustrates MD tear strength. Among the samplescomprising 75% nylon-6, the fabrics initially comprising 108 and 216islands showed the best tensile and tear performance in CD and MD,respectively. Nonwovens originally comprising 25% nylon-6 and 36 islandsdemonstrated the highest tensile and tear properties in MD, whereas thewebs comprising 25% nylon-6 and 360 islands had the highest values ofthe tensile and tear strength in CD. Visual examination of thehydroentangled substrates that exhibited the best performance indicatedthese webs had the most uniform structure and showed no delaminatingduring mechanical testing in contrast to other samples examined. Thisindicates web uniformity and bonding efficiency were prevalent factorsinfluencing the mechanical properties of the hydroentangled nylon-6webs.

Example 6 Effect of Thermal Bonding Before and after PLA Sea Removal onFabric Mechanical Properties

Fabric mechanical properties were evaluated to compare fabrics preparedaccording to the present invention without heat bonding with fabricsprepared using heat bonding. Three fabrics were prepared as described inExample 1. The multicomponent fibers were prepared using PLA as the seacomponent and nylon-6 as the island components. The fiber was extrudedto comprise 108 island components with a 50/50 I/S ratio. The fabricswere hydroentangled using three passes. The calendaring device was setfor point bonding of the fabric. The results are provided below in Table5.

TABLE 5 MD CD Tensile Tear Tensile Tear Strength Strength StrengthStrength Bonding Conditions (N) (N) (N) (N) Hydroentangling followed by168.7 83.4 51.0 151.1 PLA removal Hydroentangling followed by 178.5 49.152.0 104.0 PLA removal and subsequent Calendaring at 145° C.Hydroentangling followed by 69.7 27.5 29.4 43.2 Calendaring at 190° C.and subsequent PLA removal

As seen above, thermal bonding after removal of the sea component wasuseful for increasing tensile strength (particularly MD tensilestrength). However, fabrics prepared according to the invention withoutthermal bonding otherwise outperformed the thermally bonded fabrics.This is particularly seen in the sample where calendaring was carriedout before removal of the sea component. The effect of thermal bondingis further illustrated in FIG. 29, which shows the sample calendaredafter removal of the sea component, and FIG. 30, which shows the samplecalendared before removal of the sea component.

The diamond-shaped thermal bond points in FIG. 29 are clean anddistinct, while the bond points in FIG. 30 are more irregular and showmarked delamination. This is further illustrated in FIG. 31, which showsa more detailed view of one bond point from FIG. 29. Likewise, FIG. 32shows a more detailed view of one bond point from FIG. 30. As clearlysee in FIG. 32, thermal bonding prior to removal of the sea componentcan be a detriment to the overall integrity of the fabric, particularlyat the bond points.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions. Therefore, it is to be understood that theinventions are not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A nonwoven spunbonded fabric, comprising:mechanically entangled multicomponent fibers, said multicomponent fibershaving a predetermined average diameter and having an islands in the seaconfiguration comprising a plurality of island components comprising afirst polymer surrounded by a sea component comprising a second polymer;said fabric being devoid of thermal bonds.
 2. The fabric of claim 1,wherein the multicomponent fibers comprise an outer surface, and whereinthe sea component completely surrounds the island components such thatnone of the island components form any portion of the outer surface ofthe multicomponent fibers.
 3. The fabric of claim 2, wherein the seacomponent completely surrounds the island components such that the seacomponent forms a sheath around the island components, the sheath havinga thickness measured between the outer surface of the multicomponentfiber and the islands nearest the outer surface of the multicomponentfiber.
 4. The fabric of claim 3, wherein the sheath has a thickness thatis greater than or equal to an average diameter of the islandcomponents.
 5. The fabric of claim 1, wherein said multicomponent fiberscomprise extruded fibers having an average diameter in the range ofabout 5 μm to about 25 μm.
 6. The fabric of claim 1, wherein saidmulticomponent fibers comprise extruded fibers having an averagediameter in the range of about 10 μm to about 20 μm.
 7. The fabric ofclaim 1, wherein said multicomponent fibers comprise extruded fibershaving an average diameter in the range of about 50 nm to about 5 μm. 8.The fabric of claim 1, wherein the island components have an averagediameter in the range of about 50 nm to about 1 μm.
 9. The fabric ofclaim 8, wherein the island components have an average diameter in therange of about 100 nm to about 800 nm.
 10. The fabric of claim 1,wherein said multicomponent fibers comprising between about 2 and about1000 island components.
 11. The fabric of claim 1, wherein saidmulticomponent fibers comprise between about 36 and about 400 islandcomponents.
 12. The fabric of claim 1, wherein said multicomponentfibers comprise an island/sea ratio in the range of about 75/25 to about25/75.
 13. The fabric of claim 1, wherein the first polymer is differentfrom the second polymer.
 14. The fabric of claim 1, wherein the firstpolymer comprises a polyamide.
 15. The fabric of claim 1, wherein thefirst polymer comprises a polymer selected from the group consisting ofpolyolefins, polyamides, polyesters, thermoplastics, and combinationsthereof.
 16. The fabric of claim 1, wherein the second polymer comprisesa polymer selected from the group consisting of polyvinyl alcohol,poly(lactic) acid, co-PET, and combinations thereof.
 17. The fabric ofclaim 1, wherein the first polymer comprises nylon and the secondpolymer comprises PLA.
 18. The fabric of claim 1, wherein the spunbondedfabric comprises a first surface and an opposing surface, and whereinsaid mechanically entangled multicomponent fibers are present only oneof the surfaces.
 19. The fabric of claim 1, wherein the spunbondedfabric comprises a first surface and an opposing surface, and whereinsaid mechanically entangled multicomponent fibers are present on thefirst surface and the opposing surface.
 20. The fabric of claim 1,wherein the fabric exhibits an MD tensile strength of at least about 25N when normalized to a 100 g/m² basis.
 21. The fabric of claim 1,wherein the fabric exhibits a CD tensile strength of at least about 25 Nwhen normalized to a 100 g/m² basis.
 22. The fabric of claim 1, whereinthe fabric exhibits an MD tear strength of at least about 25 N whennormalized to a 100 g/m² basis.
 23. The fabric of claim 1, wherein thefabric exhibits a CD tensile strength of at least about 50 N whennormalized to a 100 g/m² basis.
 24. The fabric of claim 1, wherein thefabric exhibits an absorbent capacity of at least about 5 cm³/g.
 25. Thefabric of claim 1, wherein the fabric exhibits an absorbency rate of atleast about 0.025 cm³/g·s.
 26. The fabric of claim 1, wherein the fabricexhibits an air permeability of at least about 5 (cm³/s)/cm².
 27. Anarticle prepared using the fabric of claim 1, wherein the article isselected from the group consisting of liquid filters, air filters,barrier fabrics, technical wipes, personal care wipes, and artificialleather products.